ould it chance that before the close of another century the
ether should have taken its place along with these discarded creations
of the scientific imagination of earlier generations. The philosopher of
to-day feels very sure that an ether exists; but when he says there is
"no doubt" of its existence he speaks incautiously, and steps beyond the
bounds of demonstration. He does not KNOW that action cannot take place
at a distance; he does not KNOW that empty space itself may not perform
the functions which he ascribes to his space-filling ether.

Meantime, however, the ether, be it substance or be it only dream-stuff,
is serving an admirable purpose in furnishing a fulcrum for modern
physics. Not alone to the student of energy has it proved invaluable,
but to the student of matter itself as well. Out of its hypothetical
mistiness has been reared the most tenable theory of the constitution of
ponderable matter which has yet been suggested--or, at any rate, the
one that will stand as the definitive nineteenth-century guess at
this "riddle of the ages." I mean, of course, the vortex theory of
atoms--that profound and fascinating doctrine which suggests that
matter, in all its multiform phases, is neither more nor less than ether
in motion.

The author of this wonderful conception is Lord Kelvin. The idea was
born in his mind of a happy union of mathematical calculations with
concrete experiments. The mathematical calculations were largely the
work of Hermann von Helmholtz, who, about the year 1858, had undertaken
to solve some unique problems in vortex motions. Helmholtz found that
a vortex whirl, once established in a frictionless medium, must go on,
theoretically, unchanged forever. In a limited medium such a whirl may
be V-shaped, with its ends at the surface of the medium. We may imitate
such a vortex by drawing the bowl of a spoon quickly through a cup
of water. But in a limitless medium the vortex whirl must always be
a closed ring, which may take the simple form of a hoop or circle, or
which may be indefinitely contorted, looped, or, so to speak, knotted.
Whether simple or contorted, this endless chain of whirling matter (the
particles revolving about the axis of the loop as the particles of a
string revolve when the string is rolled between the fingers) must, in
a frictionless medium, retain its form and whirl on with undiminished
speed forever.

While these theoretical calculations of Helmholtz were fresh in his